Differential Flatness Control Approach for Fuel Cell/Solar Cell Power Plant with Li-Ion Battery Storage Device for Grid-Independent Applications

A solar cell/hydrogen energy power plant, fed by photovoltaic (PV) and fuel cell (FC) sources with a Li-ion battery (Bat) storage device and suitable for distributed generation applications, is proposed herein. The PV is used as the main source; the FC acts as a backup, feeding only the insufficiency power (steady-state) from the PV; and the battery functions as an auxiliary source and a short-term storage system for supplying the deficiency power (transient and steady-state) from the PV and the FC. For high-power applications and optimization in power converters, four-phase parallel converters are implemented for the FC converter, the PV converter, and the battery converter, respectively. Using the non-linear estimation based on the differential flatness property for dc bus energy regulation, we propose a simple solution to the fast response and stabilization problems in the power system. This is the main contribution of this research paper. The prototype small-scale power plant implemented was composed of a PEMFC system (1.2 kW, 46 A [Nexa (TM) Ballard Power Systems]), a PV array (0.8 kW [Ekarat Solar Cell]), and a Li-ion module (11.6 Ah, 24 V [SAFT Technology]). Experimental results validate the excellent control algorithm during load cycles.